1. Field of the Invention
The invention relates to trailing arm suspensions for supporting a vehicle trailer. In one of its aspects, the invention relates to a trailing arm suspension with an anti-creep device that prevents the translational movement of a parked trailer during loading of the trailer.
2. Description of the Related Art
Trailing arm suspensions are commonly used in heavy-duty vehicles such as tractor/trailers. A typical trailing arm suspension comprises a hanger bracket and an air spring both having one end mounted in spaced relationship and extending downwardly from a frame rail. A trailing arm extends between the hanger bracket and the air spring. One end of the trailing arm is rotatably mounted to the hanger bracket, usually by an elastomeric bushing. The other, opposing, end of the trailing arm is mounted to a bottom portion or piston of the air spring. The trailing arm is adapted to mount a vehicle axle, which rotatably supports the wheels. Any vertical movement of the wheels in response to changes in the road surface is translated into a rotation of the trailing arm with respect to its pivotal mounting at the hanger bracket. The air spring dampens the pivotal movement of the trailing arm.
Tractor-trailer configurations commonly use air-operated brakes that are supplied pressurized air from an air reservoir tank supplied by a compressor on the tractor. The air-operated brakes are well known and include an emergency brake utilizing a large force compression spring that is compressed by the pressurized air to release the emergency brake. The intentional or accidental loss of the pressurized air to the emergency brakes results in their application. The brakes also include an air-operated service brake for normal braking operations.
The air springs and air-operated brakes are all pressurized by the same air reservoir tank. For safety purposes, the air springs and air-operated brakes are pressurized by discrete plumbing systems or lines to ensure that the brakes are given priority. The air supply to the air springs is terminated when the pressurized air supply drops below a predetermined pressure to ensure a sufficient supply of air to operate the brakes. Within the brake system, the emergency brakes are pressurized by a different line than the service brakes.
It is common for trailers having a trailing arm suspension to incorporate a height control valve to set the ride height of the trailer with respect to the ground. The height control valve is typically connected to the air spring supply line. The height control valve has three positions: a fill position, a neutral position, and an exhaust position. In the fill position, the height control valve fluidly connects the pressurized air source to the air spring to inflate the air spring and raise the frame rail relative to the trailing arm. In the exhaust position, the air spring is fluidly connected to the atmosphere to permit the exhausting of pressurized air from the air spring to deflate the air spring and lower the frame rail relative to the trailing arm. In the neutral position, the air spring is neither connected to the source of pressurized fluid nor to the atmosphere.
The height control valve is actuable between the filled, neutral, and exhaust positions by a rotatable arm that is mechanically linked by an adjustable mechanism, such as a variable length linkage, to the trailing arm. By adjusting the linkage between the trailing arm and the rotatable arm of the height control valve, it is possible to set the ride height of the trailer to a predetermined level.
In addition to a height control valve, trailers typically include an anti-creep device to prevent the trailer from creeping away from the loading (lock as the trailer is being loaded. The creeping phenomenon is attributable to weight that is added to the trailer when the pressurized air source is unavailable, which is typical during loading. Without the availability of additional pressurized air, the air springs cannot be inflated to compensate for the reduced height attributable to the increasing trailer weight during loading. The reduced height is attributed to the relative movement of the frame toward the axle upon the addition of weight to the trailer. The resulting effective pivoting of the frame with respect to the rotates the wheels since the wheels are in contact with the ground, which drives the trailer away from the loading dock. This is known as the creeping phenomenon.
One type of class of anti-creep devices comprises a rotatable arm that is coupled to an air actuator controlled by supplied air by the air spring system and actuated by the brake system. When the vehicle is operated under normal conditions, the rotatable arm is kept in a raised position generally parallel and beneath the frame rail. When the trailer is being loaded and the emergency brakes are exhausted, the rotatable arm is rotated to an extended position where its end lies just above the trailing arm. Any relative movement of the frame rail and the trailing arm will be stopped once the rotatable arm contacts the trailing arm.
The rotatable arm anti-creep devices have known disadvantages. First, if the trailer, especially a loaded trailer, is unlooked from the tractor and allowed to sit for an extended period of time, the height control valve can temporarily xe2x80x9cfreezexe2x80x9d prohibiting the introduction of pressurized air from the trailer""s air reservoir tank to the air springs to raise the trailer to its predetermined ride height. This problem is exacerbated in that over extended periods of time, the pressurized air will slowly leak from the pressurized air system resulting in a very slow and gradual lowering of the vehicle ride height. When one or both of these conditions occur, the arms of the anti-creep device, which are in the extended position, can be bound or compressively retained in the extended position.
The coupling of the tractor to the trailer and the corresponding pressurization of the air systems will not always overcome the temporary freezing of the height control valve, leaving the suspension in an inoperable state. The subsequent jarring of the trailer during initial movement will free the frozen height control valve and the height control valve can operate normally to raise the trailer and free the arms. If the height control valve remains frozen, the suspension will not function properly and can be damaged. Second, during the backing of the trailer toward the dock, it is common for the tractor operator to quickly and forcefully apply the brakes when the trailer has reached the loading position relative to the dock and simultaneously apply the emergency brake, which immediately moves the arms of the anti-creep device to the extended position. Depending on the timing between stopping the rearward movement of the trailer and the application of the emergency brakes, it is possible for the momentum of the trailer to temporarily lower the rear of the trailer relative to the trailing arm, preventing the full extension of the rotatable arm of the anti-creep device. Alternatively, it is possible for the rotatable arm of the anti-creep device to be fully deployed but the rearward momentum of the trailer lowers the height of the trailer and compresses the arm between the trailer frame and the trailing arm. If the trailer air reservoir tank is not pressurized above the safety threshold, then no air is available to raise the trailer to the preferred height.
It is desirable to prevent the binding of the anti-creep device arms between the trailer frame and the trailing arm to avoid damaging the suspension.
The invention addresses the shortcoming of the prior art in a trailing arm suspension with a height control valve in combination with an anti-creep device by means of an automatic reset mechanism that pressurizes the air spring until the rotatable arm is free to rotate to the retracted position, even if the ride height is set too low. The automatic reset mechanism adjusts the trailer height to prevent the binding of the trailing arm suspension and the anti-creep device when the height control valve is improperly adjusted.
According to the invention, a trailing arm suspension for supporting ground-engaging wheels relative to a vehicle frame has a trailing arm with a forward portion adapted to be mounted to the vehicle frame for pivotable movement with respect thereto. An air spring is mounted at one end to the trailing arm and is adapted to be mounted at another end to the vehicle frame. An axle is connected to the trailing arm for carrying the ground-engaging wheels. A pneumatic air supply system for pressurizing the air spring includes a height control valve for controlling the introduction of exhaustion of pressurized air to and from the air spring to control the relative position of the vehicle frame with respect to the axle. An anti-creep mechanism is adapted to be mounted to the vehicle frame and is movable between a retracted position where the trailing arm is free to pivot relative to the vehicle frame and an extended position where the trailing arm is substantially prevented from pivoting toward the vehicle frame. An auxiliary air supply system for pressurizing the air spring includes a second control valve for controlling the pressure to the air spring. An actuator is responsive to the movement of the anti-creep mechanism between the extended and retracted positions for closing the second control valve when the anti-creep mechanism is in the retracted position and is further responsive to movement of the anti-creep mechanism between the retracted and extended positions for opening the second control valve.
In a preferred embodiment, the arm is adapted to be pivotally mounted to the vehicle frame and the arm extends between the vehicle frame and the trailing arm to block the relative pivotable movement of the trailing arm toward the frame. The actuator preferably comprises a link coupling the arm to the second control valve. When the arm is the retracted position, the link closes the control valve to prevent pressurization of the air spring. When the arm is in the extended position, the link opens the control valve for pressurization of the air spring from the auxiliary air supply.
In a preferred embodiment, the control valve comprises a body having an inlet port fluidly connected to the auxiliary air supply system, an outlet port fluidly connected to the air spring and a lever movable between a first position at which the inlet and outlet ports are fluidly blocked and a second position at which the inlet and outlet ports are fluidly connected. The link is connected to the lever and moves the lever between the first and second positions as the arm is moved between the retracted and extended positions.
In a further embodiment of the invention, the anti-creep mechanism further comprises a rod adapted to be mounted for rotation about an elongated axis thereof to the vehicle frame and the arm is fixedly mounted to the rod whereby rotation of the rod about its longitudinal axis moves the arm between the retracted and extended positions.
The anti-creep mechanism further comprises in a preferred embodiment an air-operated actuator connected to the rod and fluidly connected to the pneumatic air supply system. The pneumatic air supply system pressurizes the air-operated actuator to rotate the rod to a retracted position and thereby rotate the arm to the retracted position. When the pneumatic air supply system is shut down, the rod rotates to an extended position at which the arm is rotated to the extended position.